Electric filter arrangement



pnrl ML, l W HAGEN ELECTRIC FILTER ARRANGEMENTS Filed Oc't. l5, 1938 2 She'eis-Sheet l B, 1941. W1 HAGEN ELECTRIC FILTER ARRANGEMENTS Filed Oct. l5, 1938 2 Sheets-Sheet 2 l Aff? Patented Apr. 15, 17941 UNITED STATES PATENT oFF-ica ELECTRICJFILTER ARRANGEMENT Application October 15, 1938, Serial No. 235,185 In Germany October 19, 1937 1 Claim.

It is well known to transfer broadcast programmes, alarm signals and the like over wire networks, such as telephone networks, by means of high frequency carrier currents. In systems of this kind electric filter circuits must be provided in order either to separate the currents of dierent frequencies from each other or to bring them together, as the case may be. Such filter circuits are required in the exchanges, for instance, in order to impress the high frequency wire radio currents upon the telephone lines, and they are necessary also at the subscribers stations in order to separate the low frequency telephone talking currents from the high frequency wire radio currents.

The usual electric lter circuits comprise a high-pass filter and a low-pass filter. The highpass filter is to be of the least possible attenuation in relation to the high frequency currents while being of very great attenuation as regards the low frequency talking currents, in order, for instance, to preclude that the telephone conversations can be listened to at the lines of the high frequency receiving apparatus. The low-pass filter on the contrary is to avoid high frequency currents arriving in the telephone apparatus in which they would be modulated with the talking currents, thus becoming audible in the high frequency receiver.

Also, both filters must be of a construction symmetric to earth in order that no disturbing alternating voltages shall be received, and further it is desirable, that it shall be possible to load the connected circuits either symmetrically or asymmetrically without impairing the line symmetry.

Furthermore it is necessary that the number of the constructional elements employed in the Iilters and hence the space requirements be as low as possible.

These filter circuits in general comprise socalled condenser lines, that is, filters having condensers arranged in the line wires and induct ances disposed between these. In addition to such condensers and inductances a transformer is necessary in order to suit the resistance of the line to the input circuit of the receiver.

The invention has for its object to simplify lter circuits of this kind. In accordance with the invention the inductances of the high pass filter which are located between the line wires are arranged to constitute an iron core transformer, the two inductive parts of the lter circuit thus being comprised in a single member.

In the accompanying drawings Figs. l to 4 are n age influences.

diagrammatic views eachshowing a representative example of the invention.

A, B denote supply wires, constituting a telephone subscribers line, for instance.

In the arrangement represented in Fig. 1 the electric lter circuit joined to the lines A, B comprises a high pass filter I and a low pass filter 2. To lter I a broadcast or wire radio receiver, for example, is connected. Joined to filter 2 may be a telephone set 4 of the customary type. Filter 2 has four inductances 5, 6, 1, 8, included in the line A, B, and also comprises two condensers 9, Iil. earthed at the center point between them. The inductances 6, 'I are coiled around the same core,

Filter I has four condensers I2, I3, I4. In accordance with the invention the inductance I 5 located between the wires A, B is a transformer, so that member I5 while forming part of the lter chain at# the same time acts to effect a mutual adaptation of the line resistance and the resistance of apparatus 3.

Another advantage of this arrangement is, that only the condensers I3, being directly connected with the line, should be protected from high Volt- The output condensers I2, I4 need only stand a small test voltage, since the transformer prevents the high voltage energy from influencing them.

The arrangement shown in Fig. 1 may according to Fig. 2 be simplied by constructing the high pass lter I as a transformer I6 whose windings are interrupted in the middle by a condenser I1 or I 8. These two condensers, in order to obtain the same lter eiect as in the case of Fig. 1 must each have half the capacity of the condensers provided in the high pass lter of the arrangement shown in Fig. 1.

, In the arrangement represented in Fig. 3 the high pass filter I has two condensers I 9, 20 which are arranged asymmetrically, being both included in one wire of the line. The earth capacities E' of these condensers cause the arrangement as a whole to be asymmetrical in relation to earth. In accordance with the invention transformer 2| is in its turn rendered asymmetric with respect to earth and in such manner that the earth capacities E" of its windings act to compensate the earth capacities El', the said asymmetries thus being without effect.

The arrangement shown in Fig. 4 isof the greatest possible simplicity. I-Iigh pass lter I here comprises a transformer 22 and a condenser 23. This transformer should be so calculated as to constitutel in conjunction with the condenser a half filter member. Furthermore it should be so constructed that its winding 2l, connected din rectly with the receiving apparatus 3, is absolutely symmetrical to earth while its input winding presents a ground asymmetry E" by which the earth capacity E' of condenser 23 is compensated,

What is claimed is:

A compact line-to-terminal-apparatus lter for connection directly across a symmetric line on one side and directly across a terminal apparatus on the other side and adapted to effect a substantially high pass transmission therebetween without impairing the line symmetry while simultaneously mutually matching the line resistance and the resistance of the terminal apparatus, which consists substantially of an iron-core twowinding transformer of which one Winding is connected to said line and the other to said apparatus, one of said windings having a greater earth capacity at one end than at the other end and the Whole transformer effectively constituting an inductive shunt arm for the lter while simultaneously eiecting a resistance matching transformer coupling between said line and said apparatus, and a single condenser connected in series with said Winding having the greater earth capacity at one end, said condenser being connected in series with said winding at that end having the lower earth capacity whereby the asymmetry of said winding in relation to earth neutralizes the asymmetry with respect to earth .resulting from the earth capacity of said condenser.

WOLFGANG HAGEN. 

